This application claims the priority of German patent document 199 13 794.3, filed Mar. 26, 1999.
The invention relates to a vehicle having a transmission line for at least two driving wheels, an internal-combustion engine drive and a fuel cell system drive.
A known hybrid drive for a vehicle disclosed in British Patent Document GB 1447 835 consists of an internal-combustion engine drive and a fuel cell system drive. The fuel cell system drive contains an electric motor whose shaft is connected at one end with the drive shaft of the internal-combustion engine and at the other end with a clutch. The clutch is followed by a transmission line having a transmission, a cardan shaft, a differential gear, wheel shafts and driving wheels. The internal-combustion engine and the fuel cell are supplied with hydrogen by a common fuel source, by way of respective supply lines. Each supply line has a control valve connected to an electric control system which is mechanically connected with a foot pedal; the position of the foot pedal controls the operation of the two control valves in the supply lines. For pedal positions assigned to lower driving powers for the vehicle, the control system opens up the control valve in the supply line for the internal-combustion engine, while for pedal positions assigned to higher driving powers, the control system opens up the control valves in both supply lines for the internal-combustion engine and the fuel cell.
So that the fuel cell will be able to provide power without any interruption, an additional control unit allows the internal-combustion engine to operate at a low power output for the vehicle in the idling mode, while the fuel cell emits power. In the case of a higher power demand, both drives operate together. In the idling mode, sufficient fuel is fed to the internal-combustion engine that it does not act as a brake for the electric motor which generates the driving power.
Another known vehicle has an electric motor, a fuel cell, a compressor for feeding air to the fuel cell, an electric motor for driving the compressor, a reformer, a fuel tank for liquid fuel, a water tank and an evaporator. The liquid fuel and the water are changed in the evaporator into the gaseous state and are then guided to the reformer. There, while heat is supplied, by means of a catalytic burner, hydrogen, carbon dioxide and carbon monoxide are formed. The hydrogen-containing gas thus formed is fed to the fuel cell together with pressurized air (See German Patent Document DE 44 12 451 01).
Fuel cell systems which include a gas generator for generating hydrogen from a liquid fuel, have a number of disadvantages in comparison to fuel cell systems which are fed from tanks with gaseous hydrogen. Elimination of these disadvantages requires significant additional expenditures, and is not completely successful.
In this context, mainly cold starting behavior is problematic. Since the gas generating system becomes operable (that is, it generates hydrogen containing gas) only after a defined higher operating temperature is reached (depending on the type of fuel), it must first be heated after the vehicle is started. This results in a waiting time between the vehicle start and its readiness to be operated. Moreover, the generation of thermal energy to heating up of the gas generating system consumes fuel while the vehicle is idle.
In order to avoid the above-mentioned disadvantages, either an additional storage unit must be provided, or a process for generating hydrogen without high temperatures (that is, at ambient temperature), can be used. A suitable hydrogen generating process which operates at an ambient temperature, however, is not known.
The storage unit, which may consist, for example, of an electric battery, a supercondenser or an additional hydrogen tank, must have a sufficient charge or filling before the start of the operation. However, after longer stoppage times, this may no longer be the case. In the case of a hydrogen generating process which also operates at low temperatures, the expenditures are increased.
One object of the invention is to provide a fuel cell system fed with liquid fuel, and a process for operating a vehicle, which permit the vehicle to start to drive immediately, without any energy removal from an additional gas accumulator for the fuel cell.
This and other objects and advantages are achieved by the vehicle according to the invention, which has at least one transmission line for driving the vehicle wheels, together with an internal-combustion engine drive which can be coupled to the transmission line, and a fuel cell system which includes a gas generating device for generating a hydrogen-containing gas from a fuel for the fuel cell, at higher temperatures. Devices are also provided for transmitting heat from the internal-combustion engine drive into the gas generating device and into the fuel cell, as well as a control system, by which assemblies for feeding fuel and air to the fuel cell system (after the gas generating device is heated up) and to the fuel cell, can automatically be switched to working temperatures. The transmission line consists of those components which are situated between the vehicle's clutch and its driving wheels.
The internal-combustion engine drive in this case is a drive with a conventional internal-combustion engine, together with assemblies required for driving, such as the starter, the generator, the accumulator, the fuel distributor, the ignition device, etc. The internal-combustion engine drive is started conventionally, by means of an ignition key which actuates the components for starting.
Hot exhaust gases generated during operation of the internal-combustion engine heat the gas generating device and the fuel cell to operating temperatures (or to a temperature sufficient for their operation). As soon as the working or operating temperature has been reached, the supply of air and liquid fuel to the gas generating device is initiated, and the fuel cell is started with the air and the hydrogen-containing gas emitted by the gas generating device.
The vehicle also includes at least one electric driving motor which is controlled, for example, by way of an actuator, and can be coupled to the transmission line by way of a clutch, when the fuel cell generates current. Depending on the required driving power, the internal-combustion engine may cooperate with the electric driving motor, or may be uncoupled from the transmission line. Liquid fuel is preferably provided to supply energy to the internal-combustion engine drive, and to the fuel cell system.
The system according to the invention permits a vehicle which uses liquid fuel for a fuel cell system drive, to be ready to drive immediately. Thus, waiting times during the start of the operation with a cooled gas generating system can be avoided. Additional advantages of the system according to the invention are: No additional fuel requirement for heating the fuel cell system before starting to drive; increased operational reliability in that the vehicle is able to continue to drive, by means of the internal-combustion engine, in the event of a disturbance of the fuel cell system; and flexible utilization of the internal-combustion engine and the fuel cell system drive according to the requirement for additional or alternative driving power, additional current supply, etc.
It is advantageous if, after the fuel cell starts to operate, the electric driving motor can automatically be coupled to the transmission line, or if such coupling, which is to be carried out manually or by a foot pedal, can be released. As soon as the internal-combustion engine is started, its clutch connection with the transmission line and the driving wheels can be activated, whereupon the vehicle will start to move.
In an expedient embodiment, the nominal capacity of the internal-combustion engine drive is lower than that of the electric driving motor. The internal-combustion engine is required particularly for starting the vehicle when the gas generating system is cold, and for heating-up the gas generating system to the operating temperature. The power required for this purpose is low compared to that which is necessary for the various speeds, load conditions and slopes in the normal driving operation.
In particular, the internal-combustion engine drive and the fuel cell system are jointly connected to a radiator in a cooling circulating system. A joint radiator reduces the expenditures for the driving systems. In addition, before the start of its operation, the fuel cell is already heated by the internal-combustion engine to the working or operating temperature. This also saves weight at the vehicle. Another advantage is the fact that, by way of its cooling circulating system, the internal-combustion engine, has a higher temperature when it is not in operation, so that a required start of its operation for assisting the electric driving motor takes place at a higher operating temperature. As a result, the generation of pollutants (which is higher just after a start in the case of a cold internal-combustion engine) is avoided.
In another expedient embodiment, a device is provided for transmitting heat from the exhaust gases of the internal-combustion engine into the gas generating device. In particular, a bypass is arranged which extends outside the gas generating device; during the operation of the internal-combustion engine and during the operation of the fuel cell system, the bypass allows the exhaust gases to pass through, but blocks them before the start of the operation of the fuel cell system. When the fuel cell system is operating (that is, generating current), heat is created which is sufficient for the operation of the gas generating system. In order to avoid overheating during a simultaneous power output of the fuel cell and of the internal combustion engine, the exhaust gases of the internal-combustion engine will then be guided past the gas generating system.
It is advantageous for a device for transmitting heat from the exhaust gases of the internal-combustion engine to consist of at least one line which extends in the interior of the gas generating system and carries exhaust gases. This embodiment is distinguished by its simple construction.
In another advantageous embodiment, the internal-combustion engine, the gas generating device and the fuel cell are jointly connected to an exhaust gas purification system. This embodiment permits the construction of a lower-weight driving system.
The process according to the invention provides for operation of a vehicle having at least one transmission line for driving wheels and an internal-combustion engine drive which can be coupled to the transmission line, as well as having a fuel cell system with a gas generating device that generates hydrogen-containing gas for the fuel cell at higher temperatures. According to the invention, the internal-combustion engine drive is operated with liquid fuel. After starting of the internal-combustion engine, it can be coupled to the transmission line, while its hot exhaust gases heat the fuel cell system directly and/or indirectly to a temperature sufficient at least for the operation. When this temperature is reached, the fuel cell system drive is started by the feeding of fuel and air. An electric driving motor is coupled, either automatically, by foot or manual operation to the transmission line, and the internal-combustion engine is optionally uncoupled from the transmission line.
Expediently, the fuel cell and the internal-combustion engine are jointly cooled to an operating temperature, and the internal-combustion engine will thus be maintained at its operating temperature even when it is not operating. Therefore, when the internal-combustion engine is connected to augment the power of the vehicle drive, there is no high pollutant emission such as occurs in the case of a cold start.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.